title: Type VIII collagen modulates TGF-β1-induced proliferation of mesangial cells.
abstract: Mesangial cells in diabetic mice and human kidneys with diabetic nephropathy exhibit increased type VIII collagen, a nonfibrillar protein that exists as a heterodimer composed of α1(VIII) and α2(VIII), encoded by Col8a1 and Col8a2, respectively. Because TGF-β1 promotes the development of diabetic glomerulosclerosis, we studied whether type VIII collagen modulates the effects of TGF-β1 in mesangial cells. We obtained primary cultures of mesangial cells from wild-type, doubly heterozygous (Col8a1(+/-)/Col8a2(+/-)), and double-knockout (Col8a1(-/-)/Col8a2(-/-)) mice. TGF-β1 bound normally to double-knockout mesangial cells. In wild-type mesangial cells, TGF-β1 inhibited proliferation, but in double-knockout cells, it stimulated proliferation, promoted cell cycle progression, and reduced apoptosis; we could reverse this effect by reconstituting α1(VIII). Furthermore, in wild-type cells, TGF-β1 mainly stimulated the Smad pathways, whereas in double-knockout cells, it activated the MAPK and PI3K/Akt pathways and induced expression of fibroblast growth factor 21 (FGF21). Inhibiting FGF21 expression by either interfering with activation of the MAPK and PI3K/Akt pathways or by FGF21 siRNA attenuated the TGF-β1-induced proliferation of double-knockout mesangial cells. In vivo, diabetic double-knockout mice had significantly higher expression of renal FGF21 mRNA and protein compared with diabetic wild-type mice. Immunohistochemistry revealed strong expression of FGF21 in both glomerular (mesangial) and tubular cells of diabetic mice. Taken together, these data suggest that type VIII collagen significantly modulates the effect of TGF-β1 on mesangial cells and may therefore play a role in the pathogenesis of diabetic nephropathy.
authors.affiliation: Department of Internal Medicine III, University of Jena, Erlanger Allee 101, D-07740 Jena, Germany.
authors.forename: Ivonne
authors.initials: I
authors.lastname: Loeffler
authors.forename: Ulrike
authors.initials: U
authors.lastname: Hopfer
authors.forename: Dirk
authors.initials: D
authors.lastname: Koczan
authors.forename: Gunter
authors.initials: G
authors.lastname: Wolf
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D049109:Cell Proliferation / Q000187:drug effects*; D002478:Cells, Cultured; D024102:Collagen Type VIII / Q000235:genetics / Q000378:metabolism*; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D003928:Diabetic Nephropathies / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D004195:Disease Models, Animal; D005346:Fibroblast Growth Factors / Q000378:metabolism; D050527:Mesangial Cells / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology*; D051379:Mice; D018345:Mice, Knockout; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D013311:Streptozocin; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology* / Q000502:physiology
chemical_list: D024102:Collagen Type VIII; D053773:Transforming Growth Factor beta1; C414620:fibroblast growth factor 21; D013311:Streptozocin; D005346:Fibroblast Growth Factors; D019869:Phosphatidylinositol 3-Kinases; D020929:Mitogen-Activated Protein Kinase Kinases